I have P235/60/R15 all the way around.
You can use P215/65/R15 which was original equipment on 1982-1987 Z28's and 1985-1990 IROC's that came with 305 engine's and 15" wheels. That size was also on Buick Grand National's, Pontiac Grand Prix and Olds Cutlass.
Other choices are P225/60/R15 which came on 5.0L Mustang's from 1987-1993.
You can probably get P225/70/R15 to work. That came on Corvette's & Z28's and Pontiac T/A's from about 1977-1981. Police car's (Caprice, Dodge Diplomat & Ford Corwn Vic) used that size into the early 1990's. It also was on Jeep Grand Cherokee from 1993 when it debuted until the late 1990's when they started to go to 16" wheels.
Whatever you do forget about P215/60/R15. It's a very uncommon size. P 205/60/R15 used to come on Dodge Daytona's in the late 1980's but that size is hard to find as well in this day & age. The other sizes I mentioned except for the two in this paragraph should still be available and they can be bought without breaking the bank for the next 10 years.
Just my 2 cents or was that three cents for today. Good Luck!!